.out-box{
    width: 400px;
    height: 400px;
    border: 2px solid #000000;
    float: left;
}
.inside-box{
    width: 200px;
    height: 200px;
    background: red;
    color: #000000;
    text-align: center;
    font-size: 20px;
    float: left;
}